This invention relates to a butt welding machine for welding the longitudinal seam of an automotive wheel rim blank formed from a strip of metal which has been rolled into a cylinder. Typically, the rim blank is clamped between the inside and outside jaws of a pair of laterally spaced clamping assemblies located on opposite sides of a weld zone which extends along the longitudinal seam. When the blank is first clamped, its longitudinal edges are spaced laterally from each other. The clamped edges then are pressed laterally together and, while lateral pressure is being applied to the edges, an electric welding current is passed through the clamping assemblies and the rim blank to weld the edges to one another.
A welding machine of this general type is disclosed in Fencl et al U.S. Pat. No. 4,187,406. In addition to the clamping assemblies, that machine requires a separate set of swingable jaws which embrace and push against the outside of the rim blank to press the longitudinal edges together. The machine is somewhat complex and requires rather precise correlation between the clamping assemblies and the swingable jaws.
Another welding machine is disclosed in Lewis U.S. Pat. No. 2,713,626. In that machine, the edges of the rim blank are pressed together simply by rocking one clamping assembly lateral toward the other clamping assembly while the edges of the blank are clamped by the two assemblies. The inside clamping jaws of the assemblies, however, are required to pivot between open and closed positions relative to the outside jaws. Such pivoting adds to the complexity of the machine and makes it difficult to establish parallelism between the inside and outside jaws and particularly if the thickness of the rim blank varies from blank-to-blank or between various batches or blanks.